HRS cell growth can be promoted by CCR5 ligands (CCL3, CCL4, and CCL5) secreted by T cells, monocytes and tumor-educated MSCs [37,40]; by IL-3 secreted by T cells [48]; by IL-7 secreted by fibroblasts and MSCs [52]; by IL-15 secreted by monocytic/dendritic and endothelial cells [54]; by APRIL secreted by neutrophils [56]; by the membrane-bound and soluble forms of Jagged1 expressed by endothelial cells, smooth muscle cells and macrophages [63,86]; by CD137L expressed by macrophages [87]; by collagen secreted by stromal cells [88] (Table 1). The gene discussed is TNFSF9; the disease is neoplasm.